@lastangel Hi dear, thanks for your support. Part of Halo lens is made of resin material, the focus would lose a little as the temperature goes higher. So would recommend you to do the focus in 20 minutes' use. The temperature would be quite stable then. Also, Halo support autofocus, you can keep this function on and the focus easily. And Halo has the dynamic focal length compensation, it would help to focus on the background while using. Have a nice day and stay safe~